NANTUCKET, Massachusetts - Actor Kevin Spacey moved from the defense to the offense in a Nantucket courtroom on Monday.

Under pressure from multiple claims that he has sexually harassed a number of young men in the UK and the U.S., the former House of Cards star, and veteran of a number of award winning performances in movies including two that earned him an Oscar, has filed a robust, and aggressive defense against a claim that has progressed to a charge.

The claim made by a 19-year old man, who was 18 at the time, was that Spacey supplied the young man with alcohol and after doing so sexually assaulted him by groping his genitals inside and outside of his pants for three minutes.

The man says he froze when this occurred, and when Spacey took a bathroom break, he bolted from the scene. He says in his affidavitt he was encouraged to do so by a woman who had asked him if he was ok. Lawyers acting for the man have asked the woman to come forward.

The incident allegedly took place on 8 July 2016 at Club Car, a Nantucket restaurant and bar where the man worked as a busboy, however it was not reported to police until well over a year later after allegations began surfacing about the actor.

The man's mother, former Boston local television news presenter Heather Unruh, staged a press conference to protest the alleged assault, saying she had been asked to go public by her son. She said Spacey should be ashamed, and asked him how her son, who is straight, should feel as a man after being assaulted in this way.

Unruh said her son had decided to report the matter because he didn't want what happened to him to happen to anybody else.

Her press conference was held in November 2016, some sixteen months after the date of the alleged assualt.

The young man then reported the matter to the police. He has also engaged lawyers to act on his behalf and is mounting a civil lawsuit against Spacey who is worth an estimated $100 million. The criminal charge was filed on Christmas Eve, 24 December 2018.

A defiant Spacey says the claims being made against him are "patently false."

He appeared at the Nantucket court on Monday after being ordered to do so by Judge Thomas Barrett. Spacey's lawyers, Alan Jackson and Juliane Balliro had requested they be allowed to enter a plea on his behalf, however the judge refused, resulting in scores of photographers and news crews being on hand to cover the court appearance. Spacey and his lawyers however made no comment before or after the hearing, which took 10 minutes.

When asked how did he plea, Spacey's lawyers told the judge their client was submitting a not guilty plea.

The lawyers also sought an order that all phone texts and digital messaging by the alleged victim be preserved, to which Judge Barrett agreed. The judge then adjourned the hearing until 4 March, 2019. Barrett also agreed Spacey would not need to attend, but should be available by telephone if required.

Spacey, 59, is facing a charge of indecent assault and battery.

His lawyers argue, and the prosecutors agree, that the man told Spacey he was 23 and he was at college.

"His admitted actions during and immediately after the purported three-minute encounter are completely inconsistent with a victim of sexual assault," Spacey's lawyers said in a court filing.

The complaint says the young man befriended the actor after he finished work at midnight and had changed into other clothes. The man told police Spacey bought him a number of alcoholic drinks and asked him to go with the actor to his house.

The man said when the two were near the piano bar, the actor began rubbing his thigh. This he said progressed to where Spacey had unzipped his trousers and had groped him inside and outside his pants.

The man told police he was texting to his girlfriend at the time of the alleged assault and when his girlfriend said she didn't believe him, he said he sent her a video clip of the groping on Snapchat.

He said when Spacey said he was going to the bathroom, he went home.

Spacey however doesn't accept the man's version of events.

"(His) unsubstantiated, after-the-fact claims of sexual assault are patently false," his attorneys said in their filing.

They point out that the man approached Spacey, and prior to any association of the pair, the man lied to Spacey about his age. He also told the actor he was a college student at Wake Forest University, which he was not.

The filing says the man "welcomed" drinks from Spacey, accepted him putting his arm around him when near the piano, gave Spacey his phone number, and left the bar with him for a cigarette break, and returned with him to the bar.

In response to the police claim that several witnesses have confirmed they saw the pair at the restaurant that night near the piano bar, Spacey's lawyers point out that none of them have said they witnessed a sexual assault.

In reference to the Snapchat video clip, the actor's defense team argue (it) "does not show anything that could be remotely described as assaultive behavior."

Police say the man's girlfriend confirmed receiving the video of "touching the front of pants by his crotch." In an interview with police she said "she only ever saw it twice and she wasn't able to give any more description than a hand touching the front of pants."

The court orders to preserve digital transmissions between the man and his girlfriend prior to and following the alleged encounter, Spacey's lawyers say "are relevant to the issue of consent and whether lack of consent was fairly communicated."

Separately, Spacey's lawyers in a pre-trial conference with police pointed out that Spacey is accused of groping the man for about three minutes, but noted the man did not move away from Spacey nor did he tell him to stop. "That's an incredibly long time to have a strange man's hands in your pants, correct?" Spacey's lawyer Alan Jackson asked State Police Trooper Gerald F. Donovan, a member of the detective unit at the Cape and Islands District Attorney Office who investigated the case and issued the criminal complaint. "I would agree with that, yes," Trooper Donovan replied.

In rejecting the accusation of sexual assault, Spacey's lawyers in their filing said: "At best, this describes two people engaged in mutual and consensual flirtation, nothing more."

The alleged victim did not attend Monday's court appearance, nor did his mother. "We have decided as a family that we will not make any statements until trial," Unruh told NBC News. "We want to preserve the integrity of the case."

Separately the man's lawyers issued a statement Monday. "The complainant has shown a tremendous amount of courage in coming forward. Let the facts be presented, the relevant law applied and a just and fair verdict rendered," the statement said.